It really depends on what kind of soap you want to make. Is it cold process / hot process or Glycerine Soap?
Once you know which one, you then need to learn how to do it. This can be quite expensive to start with. I am assuming you already have insurance as you run a shop, but you will need to add product liability to the insurance. Ian Wallace is a good one in the UK for that and way cheaper than US prices.
Once you are ahppy with the soap you make, you will need a cosmetic chemist to certify your recipe and give you a paper so you are allowed to sell soap. Once you have insurance and certification in place, you then need to register with Trading Standards to advise them that you are now making and selling cosmetics (soap is a cosmetic in Europe) and they will come round and check your scales and your labelling compliance. After all that, you are ready to go.
You say you are running a shop. Will you be able to make enough soap to stop buying wholesale? Making soap takes time and patience. If you want to make M&P (Glycerine) soap, you will need to learn how to do all the lovely designs, if you want to make CP/HP soap, you will have to learn how to make soap, test for about a year and develop your own recipe. Then you have to make soap and wait 6 weeks for each one to be ready. Either way it will be quite an investment, you will have to buy Moulds, cutters, certificates, oils, pigments, fragrance oils and then find the time outside your shop and paperwork to do it and then fill in even more paperwork after each batch made to make sure you fall within EU rules.